A. Field of the Invention
The present invention relates generally to the field of pipe connections such as those used in the municipal water and sewer pipeline industries. More particularly, this invention relates to a sealing gasket for use in joining sections of ductile iron pipe used in such industries.
B. Description of the Prior Art
Pipes are commonly used for the conveyance of fluids under pressure, as in city water lines. They may also be used as free-flowing conduits running partly full, as in drains and sewers. Pipes for conveying water in appreciable quantities have been made of steel, cast iron, concrete, vitrified clay, and most recently, plastic including the various polyolefins and PVC.
In many applications where lengths of pipe are joined in telescoping relationship, the spigot end of one pipe is inserted into the socket end of the engaging pipe at a pipe joint or “coupling.” The socket end has an opening large enough to receive the spigot end of the mating pipe. A gasket is typically present within the socket end of the pipe which is intended to prevent leakage of fluid from the joint by forming a seal between the two pipe sections. Piping systems of the above type also typically include “fittings” as that term is defined in the industry. A fitting is a term which will be familiar to those in the relevant industries and includes a piece, often curved or at an angle, as a coupling, an elbow, a valve, a Tee, etc. used for connecting lengths of pipe or as an accessory to a pipe in a piping system for conveying fluids.
One important consideration in piping systems of the above type, whether in a straight run of pipe or at a fitting, is to provide adequate sealing at the pipe joints or couplings. In the case of ductile iron pipe installations, the sealing gasket must often perform in extreme circumstances in maintaining a proper seal at the pipe joints or couplings. Whereas the allowable clearance or raceway present between a female belled plastic pipe end and a mating male plastic spigot pipe end might be on the order of 5.5 mm, the same clearance or raceway in a ductile iron pipe system might be on the order of 90 to 125 mm. This is due, at least in part, to the difference in manufacturing tolerances and techniques utilized in manufacturing the two types of pipe. Because of the difference in dimensional tolerances which are present in ductile iron pipe systems, it would be desirable to provide some type of mechanism to prevent the gasket from blowing out of the groove provided in the belled pipe end during use. The mechanism used to prevent blow-outs of this type should also be such that it does not interfere with bending of the gasket during initial insertion of the gasket into the sealing groove provided in the belled pipe end.
A need exists, accordingly, for an improved sealing gasket for ductile iron pipelines which includes special features which insure that it will not be blown out of its associated retaining groove under high pressure situations.
A need also exists for such an improved sealing gasket for ductile iron pipelines which is cost-effective, easy to manufacture and easy to use in the field and which is dependable in operation.
A need also exists for such a gasket which has incorporated into the design special retention elements designed to prevent inadvertent blow out of the gasket at very high pressure, while at the same time allowing the gasket to retain sufficient flexibility to allow it to be bent and installed within its associated retaining groove in the belled pipe end of the pipe system.
A need also exists for such a gasket having retention elements which are easily interchanged, depending upon the expected field situation in which the pipe system will be utilized as well as other external factors in the operating environment.